Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $121.83   10.747%   $134.9231   $134.92   $134.90   $134.90  
  Purchase #2 $216.46   13.459%   $245.5934   $245.59   $245.60   $245.60  
  Purchase #3 $60.80   6.455%   $64.7246   $64.72   $64.70   $64.70  
  Purchase #4 $25.91   3.265%   $26.756   $26.76   $26.75   $26.80  
  Purchase #5 $175.61   11.187%   $195.2555   $195.26   $195.25   $195.30  
  Purchase #6 $5.90   6.592%   $6.2889   $6.29   $6.30   $6.30  
  Purchase #7 $124.70   10.429%   $137.705   $137.71   $137.70   $137.70  
  7 purchase totals = $731.21       $811.2465   $811.25   $811.20   $811.30